A Comparison between Antibacterial Activity of Propolis and Aloe vera on Enterococcus faecalis (an In Vitro Study).

Removing the bacteria, including Enterococcus faecalis, from the root canal is one of the important aims in endodontic treatment.We aimed to compare the antibacterial activity of Chlorhexidine with two natural drugs. The antibacterial activities of three different propolis extracts (alcohol concentrations: 0, 15, 40%) and Aloe vera gel on E. faecalis were compared using three methods: disk diffusion, microdilution and direct contact test. In addition to the above bacterium, the Aloe vera gel effect on Staphylococcus aureus and Streptococcus mutans was evaluated. Disk diffusion test revealed that propolis ethanolic extracts (the alcohol concentration of 15 and 40%) and Aloe vera gel have antibacterial activities but aqueous extract of propolis did not show any effect in this test. The MICs for propolis ethanolic extracts, Aloe vera gel and aqueous extract of propolis (0% alcohol) were 313 µg/ml, 750 µg/ml, 2250 µg/ml, and ≥ 500 µg/ml respectively, much higher than the Chlorhexidine one. In direct contact test, contrary to Aloe vera, all three propolis extracts showed antibacterial effects on E. faecalis. The Aloe vera gel also showed significant antibacterial effect on S.aureus and S.mutans. The hydroalcoholic extracts of propolis and Aloe vera gel had antibacterial effects on E. faecalis, however, propolis is more potent than Aloe vera. The antibacterial effect of Aloe vera on S. aureus and S. mutans is low (MIC ≥ 2250 µg/ml). Appropriate concentrations of alcoholic extracts of propolis and some fractions of Aloe vera gel might be good choices for disinfecting the root canal in endodontic treatments.

washing processes. The main reasons behind this contamination are: the complex anatomy of pulp system, existence of the secondary canals, and ability of microorganisms to survive in harsh conditions (1)(2). E. faecalis is an anaerobic grampositive bacterium which is found in periapical lesions. It is able to attack dentinal tubules and easily copes with hard condition of root canal which make it a resistant microorganisms (3). Some studies on root treated teeth have shown that E.
faecalis bacteria are prevalent up to 77% in the periradicular lesions. In fact, the involvement of this bacterium in root canal treatment failure is more likely than the primary endodontic lesions (4).
Sodium hypochlorite has been used as an intracanal irrigant, however, due to its adverse effects including damage to tissues and inducing emphysema, its used has been restricted. Chlorhexidine 2% solution is used as an intracanal irrigant with antibacterial properties and great ability to disinfect the dentinal tubules against E. faecalis, however its use has been restricted due to: discoloration of the teeth and tongue, decreasing the sense of taste, irritation of oral mucosa and mouth dryness.
Nowadays, due to its antibacterial properties, calcium hydroxide is highly used as the intracanal medication. But again, because of its high pH, this subtance is so toxic to the tissues which can lead to chronic inflammation and cell necrosis (5)(6).
Because of the cytotoxicity induced by common intracanal drugs, their inability to remove some bacteria from the dentinal tubules, and the microorganisms' resistance phenomenon, looking for new intracanal drugs especially among natural resources are highly recommended (7).
Propolis is a dense yellow-brown resin-like material which its solubility is low in water, but high in ethanol (8). This material is made from resin, bud and other parts of the plants by bees. It is used for protecting the hive against the outside pollutions and blocking the slots and cracks.
Propolis has antibacterial, antifungal, antiviral, antiinflammation, antioxidant and anti-tumor effects (8-9) and many applications for this substance in dentistry has been recently reported (7). Aloe vera, along with other 360 species, belongs to liliaceae family. This plant can grow in hot and dry weather due to its high capacity in maintaining water. Aloe vera has antibacterial, antifungal, antivirus, antiinflammation, and anti-tumor properties which make it useful in broad range of ailments including: arthritis, asthma, gastrointestinal diseases, and skin problems (e.g. psoriasis, burning and wounds).
The aim of this study was to determine the antibacterial potency of Aloe vera compared to propolis and Chlorhexidine. Also, the effect of ethanol concentration on antibacterial activity of hydroalcoholic extracts of propolis was investigated.

Propolis hydroalcoholic extraction
Propolis was dispersed in absolute ethanol (500 mg in 50 ml) at 37ºC using magnet stirring for liquid was filtered and centrifuged at 22ºC for 10 minutes (800g). These extracts were kept in the fridge (less than 1 week) and by warming up to 37ºC any precipitate was dissolved before use.

Aloe vera physicochemical analyses
Aloe vera gel was kindly gifted by Barij Essence (Kashan-Iran). Standard physicochemical assays including carbohydrates content, dry substance, ash weight, and capillary viscometry were performed.

The test microorganisms
The sample of standard strains of E. faecalis

Disk diffusion test
The method of Kirby-Bauer disk-diffusion was performed for this assay. Briefly sterile paper disks (6.4 mm) were soaked in the test material solutions for 10 minutes. Ethanol (15, 40%) and distilled water were used as negative control. The impregnated paper disks were placed on the surface of blood agar culture plates previously inoculated by the test microorganism (E. faecalis, S. mutans, S. aureous). The inhibition zone was measured for each test material.

Direct contact test
The test material solutions (500 µL each) were dried on the bottom of a 24-well plate. Then 50 µL of the test bacterial suspension (1.5×10 7 CFU/ml) was poured into each well and left to dry in a laminar airflow. After that, 500 µL of BHI was added to each well and the plate was incubated at 37ºC. After 24 hours, the colony count of 5 µL of each well's solution was measured.

The microdilution test
Broth microdilution test was performed as described in M27-A2 (CLSI) with minor modifications. The test material solutions was firstly diluted 50:50 in 2X BHI medium then serial dilutions were made using (100 µL) 1X BHI in each well, then 10 µL of microbial suspension (1.5×10 7 CFU/ml) was added. After 24 hours incubating at 37ºC, the last well without opacity was considered as minimum inhibitory concentration (MIC). The well with lowest concentration of the tested material, which could not lead to microbial growth (99.9% inhibition) after inoculating the blood agar plate, was considered as the minimum bactericidal concentration (MBC). Also the microdilution test was performed on Aloe vera using two additional microorganisms (S.aureus and S.mutans).

Statistical analyses
The data are presented as mean±SD and analyzed by ANOVA. In case of significance, the multi fold Scheffe comparisons and t-test were used for two by two comparisons. P < 0.05 was considered significant.

Results
The antibacterial activity of propolis hydroalcoholic extracts (with 0, 15, 40% ethanol), Aloe vera gel, and Chlorhexidine 2% on E. faecalis bacteria are compared using three methods: disk diffusion, direct contact and microdilution. In regards to Aleo vera, disk diffusion and microdilution tests, have been performed using two additional bacteria (S. aureus, S. mutans) to investigate more its antimicrobial spectrum.

Propolis and Aloe vera quality control assays
The results of some quality control tests on propolis are shown in table 1. The physicochemical analysis data of Aloe vera are shown in table 2.

Disk diffusion test
Propolis hydroalcoholic extract (with 15 and 40% ethanol) and Aloe vera gel showed antibacterial effect with no significant difference among them. However, no inhibition zone was observed with propolis aqueous extract (0% ethanol). Chlorhexidine 2% produced significantly higher inhibition zone compared to the other extracts (P< 0.001) (Fig. 1). The Aloe vera gel was less effective than Chlorhexidine 2% not only against E. faecalis but also against S. aureus and S. mutans (Fig. 2).

Microdilution test
The MIC results for propolis hydroalcoholic extracts, Aloe vera gel and Chlorhexidine 2% solution have been presented below ( Table 3).  (Table 3).

Direct contact test
The number of colonies of bacteria grown after 24 hours is shown in fig. 3

Discussion
In this study, we showed that Aloe vera gel and propolis ethanolic extracts have antibacterial activity against E. faecalis in in vitro. However, both these naturally available substances showed lower potency compared to Chlorhexidine in either disk diffusion and microdilution assays ( Table 3, Fig. 1, 2). On the other hand, propolis ethanolic extract showed high antibacterial activity against E. faecalis comparable to that of Chlorhexidine in direct contact test (Fig. 3) Table 2). In this study, we used high speed centrifugation following filtration to omit any dispersed solid material off the extract. Colloidal particles in the extract might exert direct  (8,18). These components show quite high antibacterial activity in direct contact test against E. faecalis (Fig. 3).
The anti-microbial effect of hydroalcoholic extracts of propolis in disk diffusion was less than that in microdilution, this issue might be aroused by low diffusion ability of alcohol soluble components in agar. On the other hand, since Aloe vera gel is aqueous, no such a difference was observable between its microdilution and its disk diffusion test ( Fig. 1, Table 3) In direct contact test the microorganism gets in touch with the surface of the dried material directly, hence, there is no problem with insolubility of antimicrobial components. For this reason, the aqueous extract of propolis, which contains the least amount of ethanol soluble antimicrobial components, only shows its weak antibacterial activity in direct contact test (Fig. 3).